Stretch polyester and acrylic spun yarn

ABSTRACT

The invention provides a spun yarn comprising polyester bicomponent staple fiber and acrylic staple fiber. The invention further provides a method for making spun yarns and fabrics. The spun yarn of the invention comprises at least 30 weight percent acrylic staple fiber and from 17 to 45 weight percent polyester bicomponent staple fiber comprising poly(ethylene terephthalate) and poly(trimethylene terephthalate), based on the total weight of the yarn.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to spun yarn comprising polyester staplefiber and acrylic staple fiber, more particularly such a yarn in whichthe polyester staple is a bicomponent that imparts high stretchproperties to the yarn.

[0003] 2. Discussion of Background Art

[0004] Bicomponent fibers are known, for example, as described in U.S.Pat. Nos. 3,671,379 and 5,922,433 and in International Published PatentApplication WO2000-73552. However, yarns made from such fibers can lackthe stretch and recovery needed for useful elastic yarns or may requirehigher proportions of such fibers than are normally required with otherelastic fibers to attain a desired level of yarn elasticity.

[0005] Economical spun yarns of polyester bicomponent staple fibers andacrylic fibers that have high stretch are still needed.

SUMMARY OF THE INVENTION

[0006] The present invention provides a spun yarn comprising at leastabout 30 weight percent acrylic staple fiber and a polyester bicomponentstaple fiber comprising poly(ethylene terephthalate) andpoly(trimethylene terephthalate), wherein the polyester bicomponentfiber is present at from about 17 to about 45 weight percent, based onthe total weight of the yarn. In a preferred embodiment, the yarn of theinvention contains at least about 50 weight percent acrylic fiber, basedon the total weight of the yarn. The balance of the yarn content may beany conventional staple fiber. For example, the spun yarn of theinvention may contain conventional poly(ethylene terephthalate) staplefiber.

[0007] The invention also provides a process for making such a spunyarn, comprising the steps of providing the bicomponent staple fiber;providing the acrylic staple fiber; combining by intimate blending theacrylic and the bicomponent staple fibers so that the resulting 1mixture contains at least about 30 weight percent acrylic staple fiberand about 17 to about 45 weight percent polyester bicomponent fiberbased on the total weight of the yarn; carding the blended fibers toform a card sliver; drawing the card sliver; doubling and redrawing thecard sliver; converting the drawn sliver to roving; and ring-spinningthe roving to form the spun yarn.

[0008] The invention further provides a fabric selected from the groupconsisting of knits and wovens, comprising such a spun yarn as made bysuch a process.

BRIEF DESCRIPTION OF THE FIGURE

[0009] The FIGURE shows a schematic cross-section of a spinneret packuseful in making bicomponent polyester fiber tow.

DETAILED DESCRIPTION OF THE INVENTION

[0010] It has now been found that spun yarn comprising acrylic staplefiber and certain proportions of a bicomponent staple fiber comprisingpoly(ethylene terephthalate) and poly(trimethylene terephthalate), hasunexpectedly high stretch characteristics even when the bicomponentstaple content is limited. The spun yarn can be used in apparel fabrics,for example in sweaters and the like, in craft yarns, and in outdoorfabrics, for example in awnings, tents, tarps, deck and lawn chairs, andthe like. The fabrics can be knit or woven.

[0011] As used herein, “bicomponent fiber” means a fiber in which twopolymers are in a side-by-side or eccentric sheath-core relationship andincludes both spontaneously crimped fibers and fibers with latentspontaneous crimp that has not yet been realized.

[0012] “Intimate blending” means the process of gravimetrically andthoroughly mixing dissimilar fibers in an opening room (for example witha weigh-pan hopper feeder) before feeding the mixture to the card or ofmixing the fibers in a dual feed chute on the card, and is to bedistinguished from draw-frame blending.

[0013] As used herein, “acrylic fiber” means a manufactured fiber inwhich the fiber-forming substance is a long chain synthetic polymercomprising acrylonitrile units and includes within its meaning acrylicfiber (at least 85 percent by weight of acrylonitrile units), modacrylicfiber (less than 85 percent but at least 35 percent by weight ofacrylonitrile units), and fiber blends thereof.

[0014] The spun yarn of the invention comprises at least about 30 weightpercent, preferably at least about 50 weight percent of acrylic staplefiber together with a polyester bicomponent staple fiber comprisingpoly(ethylene terephthalate) (“2G-T”) and poly(trimethyleneterephthalate) (“3G-T”) wherein the polyester bicomponent fiber ispresent at at least about 17 weight percent and no more than about 45weight percent, preferably at least about 25 weight percent and no morethan about 40 weight percent, based on the total weight of the yarn.When the polyester bicomponent content is lower than about 17 wt %, thestretch properties of the yarn, as indicated by the total boil-offshrinkage, can be inadequate, and when the polyester bicomponent contentis higher than about 45 wt %, there is little further improvement insuch properties, indicating that the stretch properties of the yarn donot follow the rule of mixtures in relation to the composition of theyarn, which was unexpected. The total boil-off shrinkage of the yarn canbe at least about 32%, which corresponds to about 30% elongation when a0.045 g/den (0.04 dN/tex) load is applied to the yarn after boil-off. Itis preferred that the total boil-off shrinkage be at least about 40%.The spun yarn of the invention also exhibits desirably higher bulk thanconventional acrylic spun yarns. The spun yarn may also contain aconventional staple fiber such as a convention poly(ethyleneterephthalate) staple fiber.

[0015] The bicomponent staple fiber can have a crimp development (“CD”)value of at least about 35% and can have a crimp index (“CI”) value ofat least about 10%, preferably at least about 20%, when substantiallyfree of interlacing, and no higher than about 45%, preferably no higherthan about 30%. When the CD value is lower than about 35%, the spun yarncan have too little total boil-off shrinkage to provide good stretch infabrics made therefrom. When the CI value is lower than about 10%,mechanical crimping can be necessary for satisfactory carding andspinning. When the CI value is higher than about 45%, the bicomponentstaple can have too much crimp to be readily cardable, even when blendedwith the acrylic staple.

[0016] When the CI of the bicomponent staple fiber is low in the rangeof acceptable values, higher proportions of polyester bicomponent staplefibers can be used without compromising cardability. When the CD is highin the range of acceptable values, lower proportions of bicomponentstaple can be used in the blend yarn without compromising total boil-offshrinkage. In particular, since the fiber blend level, CI, andcardability are inter-related, satisfactory cardability can be retainedeven with high CI values (for example as high as about 45%) if theamount of bicomponent fiber in the blend is low (for example as low asabout 17 wt %, based on total weight of spun yarn). Similarly, since thefiber blend level, CD, and total boil-off shrinkage are inter-related,satisfactory total boil-off shrinkage can be retained even at about 17wt % bicomponent fiber, based on total weight of spun yarn, if the CD ishigh, for example at about 55% or more.

[0017] The blended fibers can be ring-spun to form the yarn, either onthe cotton system or on a worsted spinning frame. The bicomponent staplefiber and the acrylic fiber can have a length of about at least about2.5 cm and no longer than about 10 cm. When the fibers are shorter thanabout 2.5 cm or longer than about 5.7 cm, they can be difficult to spinon a cotton spinning system, and when they are shorter than about 5 cmor longer than about 10 cm they can be difficult to spin on a worstedspinning system.

[0018] The bicomponent fiber can have a linear density of at least about0.7 dtex and preferably at least about 0.9 dtex per fiber and no morethan about 3.0 dtex per fiber, preferably less than about 2.5 dtex perfiber. When the bicomponent staple has a linear density more than about3.0 dtex per fiber, the yarn can have a harsh hand, and it can bedifficult to blend with the acrylic fiber. When it has a linear densitybelow about 0.7 dtex per fiber, it can be difficult to card.

[0019] The bicomponent staple fiber can have a weight ratio ofpoly(ethylene terephthalate) to poly(trimethylene terephthalate) ofabout 30:70 to 70:30, preferably 40:60 to 60:40. One or both of thepolyesters comprising the bicomponent fiber can be copolyesters, and“poly(ethylene terephthalate)” and “poly(trimethylene terephthalate)”include such copolyesters within their meanings. For example, acopoly(ethylene terephthalate) can be used in which the comonomer usedto make the copolyester is selected from the group consisting of linear,cyclic, and branched aliphatic dicarboxylic acids having 4-12 carbonatoms (for example butanedioic acid, pentanedioic acid, hexanedioicacid, dodecanedioic acid, and 1,4-cyclo-hexanedicarboxylic acid);aromatic dicarboxylic acids other than terephthalic acid and having 8-12carbon atoms (for example isophthalic acid and2,6-naphthalenedicarboxylic acid); linear, cyclic, and branchedaliphatic diols having 3-8 carbon atoms (for example 1,3-propane diol,1,2-propanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol,2,2-dimethyl-1,3-propanediol, 2-methyl-1,3-propanediol, and1,4-cyclohexanediol); and aliphatic and araliphatic ether glycols having4-10 carbon atoms (for example, hydroquinone bis(2-hydroxyethyl)ether,or a poly(ethyleneether)glycol having a molecular weight below about460, including diethyleneether glycol). The comonomer can be present tothe extent that it does not compromise the benefits of the invention,for example at levels of about 0.5-15 mole percent based on totalpolymer ingredients. Isophthalic acid, pentanedioic acid, hexanedioicacid, 1,3-propane diol, and 1,4-butanediol are preferred comonomers.

[0020] The copolyester(s) can also be made with minor amounts of othercomonomers, provided such comonomers do not have an adverse affect onthe benefits of the invention. Such other comonomers include5-sodium-sulfoisophthalate, the sodium salt of3-(2-sulfoethyl)hexanedioic acid, and dialkyl esters thereof, which canbe incorporated at about 0.2-4 mole percent based on total polyester.For improved acid dyeability, the (co)polyester(s) can also be mixedwith polymeric secondary amine additives, for examplepoly(6,6′-imino-bishexamethylene terephthalamide) and copolyamidesthereof with hexamethylenediamine, preferably phosphoric acid andphosphorous acid salts thereof.

[0021] There is no particular limitation on the outer cross-section ofthe bicomponent fiber, which can be round, oval, triangular, ‘snowman’and the like. A “snowman” cross-section can be described as aside-by-side cross-section having a long axis, a short axis and at leasttwo maxima in the length of the short axis when plotted against the longaxis. In one embodiment, the spun yarn of the invention comprisesacrylic staple fiber and a bicomponent staple fiber comprisingpoly(ethylene terephthalate) and poly(trimethylene terephthalate) andhaving a plurality of longitudinal grooves in the surface thereof. Sucha bicomponent staple fiber can be considered to have a “scalloped oval”cross-section which can improve the wicking properties of the polyesterbicomponent.

[0022] The polyester bicomponent staple fibers in the spun yarn of thepresent invention can also comprise conventional additives such asantistats, antioxidants, antimicrobials, flameproofing agents,dyestuffs, light stabilizers, and delustrants such as titanium dioxide,provided they do not detract from the benefits of the invention.

[0023] The bicomponent staple fiber of which the spun yarn of theinvention is comprised can have a tenacity-at-break of at least about 4dN/tex and no higher than about 5.5 dN/tex. When the tenacity is toolow, carding and spinning can be difficult, and when it is too high,fabrics made from the spun yarn of the invention can exhibit undesirablepilling. The linear density of the spun yarn can be in the range ofabout 100 to 700 denier (111 to 778 dtex).

[0024] Knit (for example warp knit and weft knit, including circularknit and flat knit) and woven (for example plainwoven and twill) stretchfabrics can be made from the spun yarn of the invention.

[0025] The process of the invention comprises a step of mixing byintimate blending an acrylic staple fiber with the polyester bicomponentstaple fiber, wherein the bicomponent staple fiber is present at a levelof at least about 17 wt % and no more than about 45 wt %, preferably atleast about 25 wt % and no more than about 40 wt %, based on the totalweight of the blended fibers.

[0026] Use of bicomponent staple fiber exhibiting “follow-the-leader”crimp in the process is preferred because such staple is believed toimprove carding due to its lower CI level. Correspondingly, it ispreferred that the bicomponent fibers in the tow precursor to the staplefiber be ‘in register’ with each other and not be ‘de-registered’.

[0027] The blended fibers can be further processed by carding theblended fibers to form a card sliver, drawing the card sliver, doublingand redrawing the card sliver up to 3 times, converting the drawn sliverto roving, and ring-spinning the roving, preferably with a twistmultiplier of 3 to 5.5 to form the spun yarn, which can have a totalboil-off shrinkage of at least about 32%.

[0028] Intrinsic viscosity (“IV”) of the polyesters was measured with aViscotek Forced Flow Viscometer Model Y-900 at a 0.4% concentration at19° C. and according to ASTM D-4603-96 but in 50/50 wt % trifluoroaceticacid/methylene chloride instead of the prescribed 60/40 wt %phenol/1,1,2,2-tetrachloroethane. The measured viscosity was thencorrelated with standard viscosities in 60/40 wt %phenol/1,1,2,2-tetrachloroethane to arrive at the reported intrinsicviscosity values.

[0029] The following method of measuring tow Crimp Development and towCrimp Index of the bicomponent fiber was used. To measure tow CrimpIndex (“C.I.”), a 1.1 meter sample of polyester bicomponent tow wasweighed, and its denier was calculated; the tow size was typically ofabout 38,000 to 60,000 denier (42,000 to 66,700 dtex). Two knotsseparated by 25 mm were tied at each end of the tow. Tension was appliedto the vertical sample by applying a first clamp at the inner knot ofthe first end and hanging a 40 mg/den (0.035 dN/tex) weight between theknots of the second end. The sample was exercised three times by liftingand slowly lowering the weight. Then a second clamp was applied at 100cm down from the inner knot of the first end while the weight was inplace between the knots of the second end, the 0.035 dN/tex weight wasremoved from the second end, and the sample was inverted whilemaintaining the tension so that the first end was at the bottom. A 1.5mg/den (0.0013 dN/tex) weight was hung between the knots at the firstend, the first clamp was removed from the first end, the sample wasallowed to retract against the 0.0013 dN/tex weight, and the (retracted)length from the clamp to the inner knot at the first end was measured incm and identified as L_(r). C.I. was calculated according to Formula I.To measure tow Crimp Development (“C.D.”), the same procedure wascarried out, except that the 1.1 meter sample was placed—unrestrained—inboiling water for 1 minute and allowed fully to dry before applying the40 mg/den (0.035 dN/tex) weight.

C.I. and C.D. (%)=100×(100 cm−L_(r))/100 cm  (I)

[0030] To determine the total boil-off-shrinkage of the spun yarns, theyarn was made into a skein of 25 wraps on a standard skein winder. Whilethe sample was held taut on the winder, a 10 inch (25.4 cm) length(“L_(o)”) was marked on the sample with a dye marker. The skein wasremoved from the winder, placed in boiling water for 1 minute withoutrestraint, removed from the water, and allowed to dry at roomtemperature. The dry skein was laid flat, and the distance between thedye marks was again measured (“L_(bo)”). Total boil-off shrinkage wascalculated from formula II:

Total B.O.S. (%)=100×(L_(bo)−L_(o))/L_(o)  (II)

EXAMPLE 1A

[0031] Poly(ethylene terephthalate) of 0.56 IV was prepared in acontinuous polymerizer from terephthalic acid and ethylene glycol in atwo-step process using an antimony transesterification catalyst in thesecond step. TiO₂ (0.3 wt %, based on weight of polymer) was added, andthe polymer was transferred at 285° C. and fed by a metering pump to a790-hole precoalescence bicomponent fiber spinneret pack maintained at280° C. Poly(trimethylene terephthalate) (1.04 IV Sorona®, a registeredtrademark of E.I. Du Pont de Nemours and Company) was dried,melt-extruded at 258° C., and separately metered to the spinneret pack.

[0032]FIG. 1 shows a cross-section of the spinneret pack that was used.Molten poly(ethylene terephthalate) and poly(trimethylene terephthalate)entered distribution plate 2 at holes 1 a and 1 b, were distributedradially through corresponding annular channels 3 a and 3 b, and firstcontacted each other in slot 4 in distribution plate 5. The twopolyesters passed through hole 6 in metering plate 7, throughcounterbore 8 in spinneret plate 9, and exited the spinneret platethrough capillary 10. The internal diameters of hole 6 and capillary 10were substantially the same.

[0033] The fibers were spun at 0.5-1.0 g/min per capillary and a polymerweight ratio of 50/50 2G-T//3G-T into a radial flow of air supplied at142 to 200 standard cubic feet per minute (4.0 to 5.6 cubic meters perminute) so that the mass ratio of air:polymer was in the range of 9:1 to13:1. The quench chamber was substantially the same as that disclosed inU.S. Pat. No. 5,219,506, which is incorporated herein by reference, butused a foraminous quench gas distribution cylinder having similar sizedperforations so that it provided ‘constant’ air flow. Spin finish wasapplied to the fibers with the conical applicator disclosed in UnitedStates Published Patent Application US2002-0051880-A1, which isincorporated herein by reference, at 0.07 wt % to 0.09 wt % based onfiber weight, and then they were wound onto packages at 1700 meters/min.

[0034] About 48 packages of the resulting side-by-side, roundcross-section fibers were combined to make a tow of about 130,000 denier(144,400 dtex) and drawn 2.63× in two stages by passing the tow around afeed roll to a first draw roll (2.37× draw in a room temperature waterbath), passing it around a second draw roll (1.11× draw) operated at 85°C. to 90° C. and 50 yards/minute (46 m/min) and supplied with a hotwater spray, heat-treated by contact with six rolls operated at 170° C.,over-fed by 10% to a puller roll, and, after application of aconventional textile finish, passed through a continuous, forcedconvection dryer operating at less than 35° C. The tow had a lineardensity of 1.3 denier/filament (1.4 dtex/filament), its tenacity was 4.8g/den (4.3 dN/tex), its CI was 34, and its CD was 53.

[0035] The tow was then collected into boxes under substantially notension and cut to 1.5 inch (3.8 cm) staple for blending with acrylicfiber in Example 1B. No mechanical crimp was applied to the bicomponentstaple fiber.

EXAMPLE 1B

[0036] The polyester bicomponent staple fiber from Example 1A andsemi-dull, 0.9 denier per filament (1.0 dtex per filament), 1{fraction(1/16)} inches (2.7 cm) long acrylic staple fiber (T-V111H, SterlingFibers, Inc.) were opened and intimately blended to obtain variousweight percents of the two fibers. The fibers were loaded into a dualfeed chute feeder which fed a Trutzschler Corp. staple card at 70pounds/hr (32 kg/hr). It was observed that samples that were 100 wt % inthe polyester bicomponent fiber could not be carded. The ambientconditions were maintained at 76° F. (24° C.), and 56% relativehumidity. The resulting card sliver was 75 grain/yard (about 5.25grams/meter). Six ends of the card sliver were collected and drafted ona Reiter (RSB) drawframe to 70 grain/yard (4.90 grams/meter). Six endsof the once-drawn 70 grain/yard sliver were subjected to the sameprocess to give twice-drawn 70 grain/yard (about 48,500 dtex) sliver,which was then converted to 0.75 hank (7795 dtex) roving on aconventional roving frame. The total draft in the roving process was6.3×, and the twist multiple was 0.7. The roving was spun on a Robertsring-spinning frame to give a 12/1 cotton count (492 dtex) spun yarnhaving a twist multiplier of 4.0. The total draft for the spinning stepwas 16.0.

[0037] The resulting spun yarns had the total Boil-Off Shrinkage(“B.O.S.”) values shown in Table I, wherein “Comp.” indicates aComparison Sample, not of the invention. TABLE I Wt % Bicomponent SampleStaple B.O.S., % Comp. 1 0 13 Comp. 2 15 30 1 30 40 Comp. 3 55 43

[0038] Interpolation of the data in Table I shows that the desiredminimum total boil-off shrinkage of 32% was obtained when thebicomponent staple fiber comprised about 17 wt % of the spun yarn andthat above about 45 wt %, little further improvement was observed.

What is claimed is:
 1. A spun yarn comprising at least about 30 weightpercent acrylic staple fiber and from about 17 to 45 weight percentpolyester bicomponent staple fiber comprising poly(ethyleneterephthalate) and poly(trimethylene terephthalate), based on the totalweight of the yarn.
 2. The spun yarn of claim 1 containing at leastabout 50 weight percent acrylic staple fiber and from about 25 to about40 weight percent polyester bicomponent fiber based on the total weightof the yarn.
 3. The spun yarn of claim 1 having a total boil-offshrinkage of at least about 32% and wherein the acrylic staple fiber isat least 85 percent by weight of acrylonitrile units.
 4. The spun yarnof claim 1 wherein the bicomponent fiber has a crimp development valueof at least about 35% and a crimp index value of from about 10% to about45%.
 5. The spun yarn of claim 1 wherein the bicomponent fiber has acrimp index value of from about 20% to about 30%.
 6. A process formaking the spun yarn of claim 1 comprising the steps of: a) providingthe bicomponent staple fiber; b) providing the acrylic staple fiber; c)combining by intimate blending the acrylic and the bicomponent staplefibers so that a resulting mixture contains from about 17 weight percentto about 45 weight percent bicomponent staple fiber and at least about30 weight percent acrylic staple fiber based on the total weight of theyarn; d) carding the blended fibers to form a card sliver; e) drawingthe card sliver; f) doubling and redrawing the card sliver; g)converting the drawn sliver to roving; and h) ring-spinning the rovingto form the spun yarn.
 7. The process of claim 6 wherein the mixturecontains from about 25 weight percent to about 40 weight percentbicomponent staple fiber based on the total weight of the yarn.
 8. Theprocess of claim 6 wherein the ring-spinning provides a twist multiplierof about 3 to 5.5, the polyester bicomponent staple fiber has a totalboil-off shrinkage of at least about 32%, and the acrylic staple fiberis at least 85 percent by weight of acrylonitrile units.
 9. The processof claim 6 wherein the bicomponent fiber has a crimp index value of atleast about 10%, the bicomponent fiber has a crimp index value no higherthan about 45%, and the bicomponent fiber has a crimp development valueof at least about 35%.
 10. A fabric selected from the group consistingof knits and wovens and comprising a spun yarn made by the process ofclaim 6.